Methods for manufacturing skeletal implants

ABSTRACT

Instrumentation for manufacturing a bone dowel from human or animal cadaveric bone and instrumentation for evaluating the suitability of the bone and/or dowel for implant use after each step of the manufacturing process is provided. Such instrumentation for manufacturing a bone dowel includes a blanking or coring apparatus, a milling apparatus a threading apparatus and a tapping apparatus. A gauge is provided to inspect and determine the suitability of the bone dowel at each step of the manufacturing process. By inspecting the dowel being manufactured after each step of the manufacturing process, time and effort which is needlessly wasted during completion of the manufacturing of dowels which are unsuitable for implant use (due to unsuitable bone and/or inaccurate machining of bone) can be avoided. Instrumentation for more accurately positioning bone and the partially manufactured dowel into the instrumentation for machining the dowel is also provided. Such instrumentation includes a gauge for positioning a piece of bone in relation to the apparatus, and mounting blocks for securing the partially manufactured dowel in relation to the milling apparatus.

[0001] This application claims priority from U.S. provisionalapplication Serial No. 60/173,646, filed Dec. 30, 1999, which isincorporated herein by reference.

BACKGROUND

[0002] 1. Technical Field

[0003] The present disclosure relates generally to methods andinstrumentation for manufacturing an implant, and more particularly tomethods and instrumentation for manufacturing and inspecting anintervertebral implant formed from cadaveric human or animal bone.

[0004] 2. Background to Related Art

[0005] Intervertebral implants which are formed from cadaveric human oranimal bone (“bone”) are well known in the art. Intervertebral implantsformed of bone having a threaded dowel configuration, i.e., cylindrical,are also well known. The manufacturing or machining of a threadedintervertebral bone dowel is an involved process which includes at leasta drilling or coring step, a milling step, a tapping step and athreading step. Due to the anatomical limitations of bone, each of themanufacturing steps must be precisely performed to produce a dowelhaving the requisite dimensions suitable for implant use. Typically, theentire manufacturing process is performed before the dowel is evaluatedor inspected for suitability for implant use. Thus, where donor bone isnot suitable for dowel manufacture or the donor bone has been improperlymachined, much time and effort is needlessly wasted in performingadditional manufacturing steps on a dowel which will never be useable asan implant.

[0006] Accordingly, a continuing need exists for methods andinstrumentation for precisely manufacturing a bone dowel from a bone andfor quickly identifying unsuitable bone early in the machining processto avoid undue waste of time and effort.

SUMMARY

[0007] In accordance with the present disclosure, instrumentation formanufacturing a bone dowel from human or animal cadaveric bone andinstrumentation for evaluating the suitability of the bone and/or dowelfor implant use after each step of the manufacturing process isprovided. Such instrumentation for manufacturing a bone dowel includes ablanking or coring apparatus, a milling apparatus, a threading apparatusand a tapping apparatus. A series of gauges are provided to inspect anddetermine the suitability of the bone dowel at each step of themanufacturing process. By inspecting the dowel being manufactured aftereach step of the manufacturing process, time and effort which isneedlessly wasted during completion of the manufacturing of dowels whichare unsuitable for implant use (due to unsuitable bone and/or inaccuratemachining of bone) can be avoided.

[0008] Instrumentation for more accurately positioning bone and thepartially manufactured dowel into the instrumentation for machining thedowel is also provided. Such instrumentation includes a gauge forpositioning a piece of bone in relation to the coring apparatus, andmounting blocks for securing the partially manufactured dowel inrelation to the milling, threading and tapping apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Preferred embodiments of the presently disclosed instrumentationfor manufacturing and evaluating intervertebral implants are describedherein with reference to the drawings, wherein:

[0010]FIG. 1 is a perspective of one preferred embodiment of thepresently disclosed blanking or coring apparatus;

[0011]FIG. 1A is a perspective view of the presently disclosed Shimpgauge;

[0012]FIG. 2 is a perspective view of a bone dowel formed by the coringapparatus shown in FIG. 1;

[0013]FIG. 3 is a perspective view with parts separated of a holdingblock of the presently disclosed dowel milling apparatus;

[0014]FIG. 4 is a perspective view of the holding block shown in FIG. 3in the assembled condition;

[0015]FIG. 5 is a side view of the holding block shown in FIG. 3;

[0016]FIG. 6 is a perspective view of one preferred embodiment of thepresently disclosed milling apparatus;

[0017]FIG. 7 is a perspective view of the bone dowel formed by themilling apparatus shown in FIG. 6;

[0018]FIG. 8 is a perspective view of the slot milling bit of themilling apparatus shown in FIG. 6;

[0019]FIG. 9 is a perspective view of the support blocks of the secondadjustment vise of the coring apparatus shown in FIG. 1;

[0020]FIG. 10 is a side view of the support block shown in FIG. 9;

[0021]FIG. 11 is a backside view of the support block shown in FIG. 9;

[0022]FIGS. 12a-12 c are perspective, front and side views of oneembodiment of the presently disclosed wall thickness GO/NO GO gauge;

[0023]FIG. 13 is a perspective view of one embodiment of the presentlydisclosed slot width GO/NO GO gauge;

[0024]FIG. 14 is a perspective view of one embodiment of the presentlydisclosed outer diameter and length gauge;

[0025]FIG. 15 is a perspective view of one embodiment of the presentlydisclosed pilot hole gauge;

[0026]FIG. 16 is a perspective view with parts separated of oneembodiment of the presently disclosed drilling holding block;

[0027]FIG. 17 is a perspective view of the bone dowel after the pilothole has been drilled and tapped;

[0028]FIG. 18 is a perspective of the holding block shown in FIG. 16 inthe assembled condition;

[0029]FIG. 19 is a perspective view of one embodiment of the presentlydisclosed tapping holding block;

[0030]FIG. 20 is a perspective view of the presently disclosed dowelthreading tool;

[0031]FIG. 21 is a perspective view of a presently disclosed dowelthread gauge; and

[0032]FIG. 22 is a perspective view of a threaded bone dowel after theouter surface has been threaded using the dowel threading tool shown inFIG. 20.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0033] The embodiment of the methods and apparatus disclosed herein arediscussed in terms of skeletal implantation and related instrumentation.It is contemplated that the present methods and apparatus formanufacturing implants find application in spinal implantationprocedures whereby a fusion implant is placed into a receiving bedformed in an intervertebral space.

[0034] In one particular embodiment in accordance with the principles ofthe present disclosure, a procedure is described for machining andinspecting fusion implants including threaded cortical dowels. It iscontemplated that the procedure may include processes such as coring adowel, milling a dowel, tapping a dowel and threading a dowel. Theseprocesses are described in greater detail below.

[0035] Referring now in detail to the drawings wherein like referencenumerals identify similar or like components throughout the severalviews, FIG. 1 illustrates aspects of a process for coring a bone dowelusing a dowel coring apparatus 10.

CORING OF A DOWEL

[0036] A pneumatic dowel blanking or coring apparatus 10 is prepared andset up for operation prior to the coring process by connecting an airsupply line 12 of dowel coring apparatus 10 to an air supply. The dowelcoring apparatus 10 includes a drill press 11. Typically, an airpressure of 100 psi and above is utilized to drive a dowel cutter 24,although coring apparatus using lesser pressures may also be used. Dowelcoring apparatus 10 is also attached to a water supply (not shown) forirrigation.

[0037] A bone shaft 14 is selected for producing the threaded corticaldowels. Bone shaft 14 is preferably a long bone shaft, i.e., the shaftof a femur, ulna, radius, tibia or fibula, although other bone may alsobe used. A cortical shaft portion 16 of bone shaft 14 includes amedullary canal 18 which is examined to determine the appropriate sizedowel cutter to be used. The dowel cutter includes a hollow cylindricalbit which must be greater in diameter than the medullary canal of boneshaft 14. It is contemplated that dowel cutter sizes such as, forexample, 6 mm, 8 mm, 10 mm, 12 mm, 14 mm, 16 mm, 18 mm, etc., may beused.

[0038] After the appropriate size dowel cutter 24 is selected, it issecured to dowel coring apparatus 10. Dowel cutter 24 is secured toshaft 26 of dowel coring apparatus 10 in a known manner and includes anannular serrated edge 14. Dowel cutter 24 is configured to penetratebone shaft 14 to blank a dowel.

[0039] Bone shaft 14 is placed into a vise assembly 28 of dowel coringapparatus 10 so that a targeted portion of shaft 14 may be blanked toproduce the dowel. A first adjustment vise 30 positions bone shaft 14along at least one axis so that canal 18 is centered with dowel cutter24. First adjustment vise 30 is manipulated by knob 31 to adjustpositioning of bone shaft 14 relative to dowel cutter 24.

[0040] A second adjustment vise 32 secures and stabilizes bone shaft 14in position for coring. Second adjustment vise 32 includes supportblocks 31 a and 31 b and inserts 34 a and 34 b. One insert is supportedon each support block. Each support block is rotatably secured to vise32 and each insert is vertically adjustable in relation to a respectivesupport block to facilitate securement of the irregular shape of boneshaft portion 16 within vise 32. Second adjustment vise 32 ismanipulated by rotating knob 33 to advance insert 34 a towards insert 34b to clamp shaft portion 16 therebetween. It is contemplated that thecomponents of the first and second adjustment vises may be movable bymotorized means. Referring to FIGS. 9-11, inserts 34 a and 34 b haveangled cavities 36 configured to receive bone shaft 14. It iscontemplated that angled cavities 36 may have alternate angularconfigurations or may comprise other geometric configurations such as,for example, elliptical, parabolic, etc.

[0041] As illustrated in FIG. 1A, a shimp gauge 38 can be employed forproperly aligning dowel cutter 24 with bone shaft 14. Shimp gauge 38includes flexible walls 39 a and 39 b which are positioned on oppositesides of and snap onto dowel cutter 24. Gauge 38 includes a cross hair40 for aligning dowel cutter 24 with the center of the medullary canal18 of bone shaft 14. More specifically, with gauge 38 positioned aboutdowel cutter 24, knob 31 can be turned to adjust the position of boneshaft 14 with respect to dowel cutter 24. Bone shaft 14 should bepositioned such that cross hair 40 is aligned with and positioned infront of the medullary canal at bone shaft 14. A window cavity 42 isformed about cross hair 40 and allows for a visual determination of theadequacy of thickness of cortical shaft portion 16, i.e., the corticalthickness of bone shaft 14 should cover the space between cross hair 40and the edge 42′ of window 42. To assist in visualization of canal 18during subsequent cuts, it is suggested to remove bone shaft 14 fromvise assembly 28 and saw off the previously cut end of cortical shaftportion 16.

[0042] Referring back to FIG. 1, during operation, the air and watersupplies connected to dowel coring apparatus 10 are activated. As asafety feature, the air and water supplies are activated only afterdowel cutter 24 is installed. A handle 44 of dowel coring apparatus 10is manipulated, such as, for example, by gradually being pulled down inthe direction indicated by arrow “A”, until dowel cutter 24, which isrotating, passes through bone shaft 14. Handle 44 is thereafterreleased. It is contemplated that manipulation of handle 44 should beperformed slowly because cutting too fast may result in off-centerdrilling, resulting in possible damage to the bone dowel. It is furthercontemplated that the components of the dowel coring apparatus may bemovable by motorized means.

[0043] Referring to FIG. 2, a bone dowel 46 is produced and is disposedwithin dowel cutter 24. Bone dowel 46, which comprises a cylindricalbone blank having a throughbore defined by medullary canal 18, may beremoved from dowel cutter 24 by hand or by the use of compressed air.

[0044] Referring to FIGS. 12A-12C, an in process check of the sidewallthickness of bone dowel 46 is performed to determine the adequacythereof. Bone dowel 46 is rinsed in water to remove loose bone particlesfrom its exterior and medullary canal 18. The cortical sidewallthickness of bone dowel 46 is checked using a gauge, such as theuniversal Wall Thickness Go/No Go gauge 48. Using a gauge end 50, whichis suitably marked, e.g., “wall”, medullary canal 18 of bone dowel 46 ispositioned about post 52 such that the thinnest portion of the bone walldefined between medullary canal 18 and the outer circumference of bonedowel 46 is permitted to freely fall between gauge post 52 and sidewall54 of gauge 48. Bone dowel 46 should not be forced or pushed betweengauge post 52 and sidewall 54, as a false measurement for adequacy ofthe bone dowel may be taken. If the dowel falls to the bottom of post52, the bone wall is too thin, and the bone dowel is rejected. Thisadequacy procedure is repeated for the opposite side of canal 18. If thebone dowel wall is unacceptable, i.e., rejected, bone shaft 14 should berechecked for centering and/or a different size, i.e., larger, dowelcutter should be used. It is contemplated that reassessment of thesuitability of the donor for bone dowel production may be reconsidered.If bone dowel 46 is acceptable, proceed in the manufacturing method.

[0045] Referring again to FIGS. 12A-12C, an in process check of corticalface wall thickness may be checked using the universal Wall ThicknessGo/No Go gauge 48. Using gauge end 56, which is suitably marked, e.g.,“Face”, medullary canal 18 of bone dowel 46 is positioned onto post 58with one end of dowel 46 positioned against face wall 60 of gauge 48 atits thinnest point. Bone dowel 46 is permitted to freely fall betweengauge post 58 and face wall 60. For the reasons discussed above, bonedowel 46 should not be forced or pushed between gauge post 58 and facewall 60. If bone dowel 46 falls to the bottom of post 58, it isrejected, i.e., the wall thickness is insufficient for dowel use. If theface wall thickness of bone dowel 46 is unacceptable, bone dowel 46 isrejected and placement of bone shaft 14 in dowel coring apparatus 10should be checked. If the bone dowel is rejected, the suitability of thedonor bone for bone dowel production may be reconsidered. If bone dowel46 is acceptable, proceed in the manufacturing method.

[0046] Referring to FIG. 14, an in process check of the outside diameterand length of bone dowel 46 is performed to determine the adequacythereof Bone dowel 46 is placed in an appropriate outside diameter andlength Go/No Go gauge 62. Bone dowel 46 is inserted into the No Go end64 of gauge 62. If bone dowel 46 is acceptable (does not fit in No-Goend 64) proceed to check bone dowel 46 in the Go end 66 of gauge 62 byinserting bone dowel 46 into the Go end 66 of gauge 62 so that a slot ofbone dowel 46 mates on a gauge boss 68 and medullary canal 18 is visiblein window 70. If bone dowel 46 fits in the Go end 66 of gauge 62, theoutside diameter is acceptable. If the outside diameter is acceptable,the length of bone dowel 46 can be checked by viewing length marker 72to determine if the length falls within an acceptable range. If thelength is acceptable, bone dowel 46 is acceptable. If bone dowel 46fails, bone dowel 46 is rejected and dowel coring apparatus 10 should bechecked. If the diameter of bone dowel 46 is acceptable, but the lengthis too long, bone dowel 46 is cut to a proper length and rechecked. Ifthe length of bone dowel 46 is too short, bone dowel 46 is rejected.

[0047] The results of the above mentioned in-process checking proceduresmay be recorded on an attached log or the like.

MILLING OF SLOT AND FACE

[0048] Referring to FIGS. 3-8, a dowel milling apparatus 74 is preparedand set up for operation during the manufacturing process by connectingan air supply 75 to dowel milling apparatus 74 (FIG. 6). Typically, apressure of 100 psi and above is utilized, although milling apparatusrequiring lower air pressures may also be used. A water supply (notshown) is connected to dowel milling apparatus 74 for irrigation.

[0049] Referring to FIGS. 6 and 8, a face and slot milling bit 76 issecured to dowel milling apparatus 74. As a safety feature, air supply75 should not be connected to apparatus 74 until the bit is secured tothe dowel milling apparatus 74. Moreover, the water supply should onlybe turned on when using dowel milling apparatus 74.

[0050] Referring to FIGS. 3-5, bone dowel 46 is inserted into anappropriately sized holding block 78. Bone dowel 46 is positioned inholding block 78 such that canal 18 is visible through block window 80and the slot is milled approximately perpendicular to canal 18. Thedepth of bone dowel 46 as seated in block 78 is set with use of a guide82 attached to block 78, as shown in FIG. 5. Set screws 84 are tightenedso that block 78 holds bone dowel 46 securely in place. Up to three bonedowels can be placed into holding block 78 at one time. It iscontemplated that holding block 78 may be alternately configured to holda single or multiple number of bone dowels.

[0051] Referring back to FIG. 6, holding block 78 is inserted into apre-centered vise 86 positioned on dowel milling apparatus 74 and vise86 is secured.

[0052] Dowel milling apparatus 74 is activated by activating the waterand air supplies. A handle 88 is manipulated to feed block 78throughface and slot milling bit 76 in the forward and reversedirections. It is contemplated that bone dowel 46 should only passthrough face and slot milling bit 76 forwards and reverse once. It isfurther contemplated that bone dowel 46 should not have reverse movementuntil face and slot milling bit 76 is completely clear of the last bonedowel in block 78. It is envisioned that prior to stopping dowel millingapparatus 74, face and slot milling bit 76 is clear of bone dowel 46.Dowel milling apparatus 74 is deactivated and holding block 78 isremoved from vise 86.

[0053] Referring to FIG. 7, after the milling step described above, bonedowel 46 has a milled slot 90 and smooth face 91. Slot 90 is orientedsubstantially perpendicular to medullary canal 18. Bone dowel 46 may beremoved from block 78.

[0054] Referring to FIG. 13, an in process check of the slot width isperformed using the universal Slot Width Go/No Go Gauge 102. Go side 104of gauge 102 is inserted into slot 90 of bone dowel 46 so that itextends through the entire length of slot 90. If gauge 102 extendsthrough the entire slot, it is acceptable. If it does not extend throughthe entire slot, bone dowel 46 is rejected. If bone dowel 46 isacceptable, proceed to check a No Go side 106 in the same manner. No Goside 106 should not fit into slot 90. Thus, if it does, slot 90 is toowide and bone dowel 46 is rejected. If No Go side 106 does not fit intoslot 90, it is acceptable. If slot 90 is rejected, milling apparatus 74should be checked. If bone dowel 46 is acceptable, proceed in themanufacturing process as follows.

[0055] Referring to FIG. 16, bone dowel 46 is placed in a holding block92 for drilling and tapping an insertion tool engaging bore 95. Bonedowel 46 is positioned with milled slot 90 on top. Up to three bonedowels can be placed into holding block 92 at one time. It iscontemplated that holding block 92 may be alternately configured to holda single or multiple number of bone dowels. Referring to FIG. 17,holding block 92 includes a drill centering device 93 having a guidebore 97 to facilitate proper positioning of a pilot hole drill bit 94for drilling hole 95 in bone dowel 46.

[0056] Drill centering device 93 includes a drill guide 96 which definesguide bore 97 and cooperates with pilot hole drill bit 94 for drillingpilot hole 95. Pilot hole drill bit 94 is secured to an electric drillor the like. Manual activation of pilot hole drill bit 94 is alsocontemplated.

[0057] Pilot hole drill bit 94 is inserted through guide bore 97 todrill pilot hole 95. Drill bit 94 is rotated clockwise until drill bit94 is observed through a holding block window (not shown) inside canal18 of bone dowel 46 and drill bit 94 turns freely. Pilot hole drill bit94 is removed by rotating drill bit 94 counter clockwise. Pilot holedrill bit 94 should not be advanced such as to engage the opposite wallof canal 18.

[0058] Referring to FIG. 15, an in process check of pilot hole 95 ofbone dowel 46 is performed to determine the adequacy of the innerdiameter thereof. To accomplish this, pilot hole 95 is visually checkedto ensure that it is approximately centered and that it passes intocanal 18. Next, the inner diameter of pilot hole 95 is checked withPilot Hole Pin Gauge 97. To accomplish this, end 98 of gauge 97 isinserted into pilot hole 95. Insertion should not be forced. If end 98extends though pilot hole 95 and into canal 18, the diameter of pilothole 95 is too large and bone dowel 46 is not acceptable. If pilot hole95 does not extend into canal 18, it can be drilled through using a handheld tool and rechecked for proper inner diameter, as discussed above.

[0059] Referring to FIG. 19, pilot hole 95 is now threaded. Toaccomplish this, a tap centering device 101 is secured to mounting block92. Tap centering device 101 is similar to drill centering device 93except that guide bore 97′ is larger than guide bore 97 to allow passageof tap 99. A tap 99 is inserted through guide bore 97′ of device 101 tothread pilot hole 95 of bone dowel 46. Tap 99 is removed after this isaccomplished by manually twisting tap 99 counter clockwise from guidebore 97′. It is contemplated that tap 99 may be operated by motorizedmeans. It is further contemplated that tap 99 should not be inserted sofar as to engage the opposite wall of canal 18.

[0060] Bone dowel 46 can now be removed from holding block 92. Bonedowel 46 is rinsed in water to remove loose bone particles from itsexterior and medullary canal 18. Referring to FIG. 18, bone dowel 46 nowincludes internally threaded pilot hole 95. Referring again to FIG. 15,an end 100 of gauge 97 may be used to check the adequacy of the threadsof pilot hole 95.

[0061] An in-process check of the cortical face wall thickness of bonedowel 46 may be conducted using the universal wall thickness Go/No Gogauge 48, similar to that described above with regard to FIGS. 12a-12 c.If the face wall thickness of bone dowel 46 is unacceptable, reject bonedowel 46 and recheck slot and face milling bit 76 and placement inholding block 78. Also reassess the suitability of the donor bone beingused for dowel production. If acceptable, proceed in the manufacturingprocess.

THREADING

[0062] Referring to FIGS. 20 and 21, bone dowel 46 can now be externallythreaded. A threading tool 108 is prepared and set up for operationduring the manufacturing process. A water supply (not shown) isconnected to threading tool 108 for irrigation. It is contemplated thatthe water supply should be activated only when threading tool 108 is inuse. It is further contemplated that threading tool 108 may beconfigured for a variety of different size bone dowels, such as, forexample, 14 mm, 16 mm, 18 mm, 20 mm, etc. Bone dowel 46 is positionedonto a loading shelf 110 within threading tool 108 through a window 112formed in tool 108. Threading tool 108 includes a plurality ofcircumferentially spaced inserts 114 having teeth for engaging andthreading the exterior cylindrical surface of bone dowel 46. A driver116 engages the slotted end of bone dowel 46 to drive bone dowel 46through threading tool 108 to form the threads on the exterior of bonedowel 46. Bone dowel 46 is placed onto driver 116 such that a tang 118located at an end of driver 116 engages slot 90 of bone dowel 46.

[0063] Tang 118 is configured to engage slot 90 of bone dowel 46 tomanually advance bone dowel 46 through tool 108 by turning a handle 120clockwise. When bone dowel 46 has passed entirely through threading tool108, it will discharge from tool 108 into a cradle or the like (notshown) positioned at one end of tool 108. Bone dowel 46 should not bebacked through threads 114 of tool 108 once it has passed throughinitially, nor should bone dowel 46 be run through twice. Referring toFIG. 21, bone dowel 46 now includes external threads 122.

[0064] Referring to FIG. 22, an in process check of threads 122 of bonedowel 46 is performed to determine the adequacy thereof. To accomplishthis, dowel threads 122 are checked using thread check gauge 124 whichincludes verifying threads 126. Verifying threads 126 are aligned withdowel threads 122 and threads 122 of bone dowel 46 are visually checkedfor gaps, unevenness, and improper fit. If gauge 124 fits threads 122without gaps and unevenness, threads 122 are acceptable. If threads 122are unacceptable, bone dowel 46 is rejected and threading tool 108 isinspected for quality and adjusted. If threads 122 are acceptable,proceed in the manufacturing process as follows:

[0065] An in-process check of the outside diameter and length of bonedowel 46 may be conducted using outside diameter and length gauge 62,similar to that described above with regard to FIG. 14. After completionof the above method, each acceptable bone dowel 46 is sterility tested,measured and packaged for use.

[0066] It will be understood that various modifications may be made tothe embodiments disclosed herein. For example, the double sided gaugesshown in FIGS. 14-17 can be formed as two separate gauges. The gaugesmay also be provided in a kit for forming bone dowels having any desireddimensions. Moreover, the coring and milling apparatus can beelectrically, hydraulically, or pneumatically actuated apparatus.Therefore, the above description should not be construed as limiting butexemplifications of the various embodiments. One skilled in the art willenvision other modifications within the scope and spirit of the claimsappended hereto.

1. A method for manufacturing a bone dowel from a bone shaft defining amedullary canal, the method comprising the following steps: a) coring acylindrical dowel from the bone shaft such that the medullary canal ofthe bone shaft forms a throughbore in the dowel having an axis which istransverse to the longitudinal axis of the dowel; b) performing anin-process inspection of wall thickness of the dowel; c) rejecting thedowel if the dowel wall thickness does not have at least predetermineddimensions suitable for implant use; and d) forwarding the dowel forfurther machining if the dowel has dimensions greater than thepredetermined dimensions suitable for implant use.
 2. A method accordingto claim 1, wherein the step of performing an in-process inspection ofthe wall thickness of the dowel includes inspecting the sidewallthickness of the dowel.
 3. A method according to claim 1 wherein thestep of performing an in-process inspection of the wall thickness of thedowel includes inspecting the thickness of the top and bottom walls ofthe dowel.